Tony Abbott is said to have told colleagues he scheduled the hospital visit to justify being in Melbourne under entitlements. Photograph: Julian Smith/AAP Image

Tony Abbott has come under pressure over his use of travel entitlements after reports he told a party room meeting that he visited a cancer centre to justify a trip to Melbourne to attend a private function the night before.

The prime minister’s office declined the opportunity to deny the damaging allegation reported by Fairfax Media, but said his travel complied with the rules and he made “no apologies” for visiting the Peter MacCallum centre.

The opposition leader, Bill Shorten, seized on the report as evidence Liberal MPs were leaking against their leader, and said the prime minister should not require an excuse to visit health facilities.

Abbott was late to the joint meeting of the Coalition parties before the resumption of parliament in Canberra on Tuesday, having held a media conference at the Peter MacCallum centre in Melbourne early in the morning stressing the government’s commitment to research.

One of Abbott’s internal critics, the backbench Liberal senator Ian Macdonald, raised the issue of Abbott’s lateness at the party meeting.

Fairfax Media said it had spoken to several government sources who were stunned to hear Abbott explain that he had scheduled the official function on Tuesday morning to justify being in Melbourne for a fundraiser on Monday night under entitlements.

The prime minister’s office did not deny the central allegation on Wednesday.

A spokesman said the Coalition party room was “a private meeting” but “all travel is within the rules”.

In a written statement, Abbott’s office said: “The prime minister is a passionate supporter of medical research and the government’s $20bn medical research future fund and he makes no apologies for his visit. Whenever the prime minister travels he maximises his visits by ensuring he participates in community events, business visits and local media.”

Shorten said it was a matter for Abbott to explain.

“I would say to the prime minister of course that you never need an excuse to visit a public hospital in Australia and that cancer centre does remarkable work,” he said.

“I think what is most telling about these reports is that there are Liberal party members leaking against the PM. A party and a leader that cannot govern itself cannot govern Australia.

“It’s not the prime minister’s travel budget which keeps me up at night; it’s his unfair budget to all Australians.”

The communications minister, Malcolm Turnbull, told the ABC that Abbott “was quite upfront and said that he had been in Melbourne and he had been to a fundraiser the night before”.

But Turnbull said he could not recall the prime minister citing that event to justify billing taxpayers.

Abbott made the comments in response to fresh criticism from Macdonald, who has regularly raised concerns over government decisions and the prime minister’s office since being demoted from the frontbench after the election last year. Macdonald has criticised the Medicare co-payment and reintroduction of indexation on fuel excise.

The Queensland MP Ewen Jones said he took exception to Macdonald’s criticism in the party room meeting.

“I stood up and said my experience in my electorate as a marginal seat holder is completely different,” Jones said. “Tony Abbott in his budget reply speech last year outlined we would be making tough decisions … at the end of the day we got elected to fix the budget.”